Which is the best reason that a geologist might carry a small dropper bottle filled with hydrochloric acid when doing fieldwork?

Hydrochloric acid reacts with carbonate minerals, often causing visible fizzing as carbon dioxide is released. A geologist can place a small drop of acid on a rock to check for carbonates. It is not used to wash samples or wear away large areas of rock, and it would be unsafe to use as an eyewash.

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